Whereas in the field on a relative straight run, it is standard to secure a track to sleepers with spikes or relatively simple hold-down assemblies, in a station or around a switch, where sleepers are not used and instead there is a poured concrete bed serving as substrate, it is preferred to use a somewhat more complex mounting assembly. Such an assembly holds the track down while permitting at least limited movement transverse of the longitudinal extension of the track, both vertically and horizontally. Such assemblies must be exceptionally rugged and have very long service lives, while still being mass producible at a reasonable unit cost since they are used in large numbers.
The existing assemblies such as described in commonly owned U.S. Pat. No. 8,056,826 and published application 2016/0298298 comprise a track plate having a top face forming a seat adapted to carry the track, a base plate or frame adapted to be anchored to the substrate, surrounding at least the lower region of the track plate, and an elastic jacket engaged between the track plate and frame and covering most of the outer surfaces of the track plate and frame. The frame is bolted down to the substrate carrying the assembly, and the rail resting in the rail seat is held down by spring clips.
Both the track plate and the frame are typically, seen from above, basically rectangular and symmetrical to a plane perpendicular to the longitudinal rail direction, and as mentioned above the frame forms a vertically throughgoing aperture in which the track plate fits when resting on the substrate either directly or via one or more thin sheets of metal and/or elastomer. Two holes are formed in diagonally opposite holes of the frame for fixing it to the substrate, and the clips fit in respective eyes that are offset to one another longitudinally of the track carried by the assembly.
Such assemblies are relatively heavy and expensive to manufacture. Since they are often mass produced and used in large quantities, it is imperative to minimize the mass of the parts and the difficulty and cost of manufacture.